They are huge, I got the 82mm ones, but they do exactly what I bought them for which is giving me a more stable and external vibration reduction when shooting video, long exposures, panoramas, etc.
Often when a tripod has the legs angled out for a low angle shot, the standard feet are barely making contact with the ground. I got these 80mm "Bigfoot!" tripod accessory and am very happy with the additional stability due to the amount of foot actually making contact with the ground.
I enjoy creating timelapses using a motorized slider and gimbal combination, and even a little tripod movement over the long process can ruin the effort. With the ongoing slider and gimbal movement and vibrations, this can be an issue, especially when setup on a bit of a slope. I think these feet solve that issue and just makes the tripod feel more attached to the ground regardless of leg angle.
These feet are relatively big compared to normal tripod feet and are about the size of the palm of my hand. The bottom part that makes contact with the ground is very grippy. The angle of each foot can be adjusted for the various tripod leg angles and uneven ground or stairs, and will sort of adjust themselves most of the time. The 50mm version of these feet probably would have been just fine, but I figured I'd go big and got the 80mm size and don't feel they're too big to lug around.
The feet mount to each leg with a standard 3/8" stud. If your tripod has removable feet, most likely it uses the 3/8" standard, regardless of manufacturer. In my pictures, I have them mounted to the Leofoto LM-405C tripod, and the pairing makes for an incredibly solid platform that feels glued to the ground. And, it's only $25, so this is an easy purchase. I'm impressed that Leofoto offers so many useful and affordable accessory choices, including a surprising number of different foot options.